Sorry to hear.
You should have attended to teh headting problem,? anyway now too late.
Try Charlton, Jayasiri at Mawanella - for a new I mean a recon engine.
AT Nugegoda Delkanda opposite the petrol shed there is a big auto spare shop, I think the name is like
Fujimi or something, they had a complete car dismanteled, also check Euro Nippon and others.
This is nopt so common engine, so if the guys got it you may be able to negotiate.
But as suggested above try Toyota Lanka, if not GS Motors at Panckikawatte,
don't worry too much, engine rebuilding is not a very issue.